Just like any RPG, one has to grind lvls in order to survive and have more mp for any class like the black mage. I to just started but this game is a early FF tradition. A pointer is to grind near a town, run low on mp? Go rest, rince and repeat. Eventually you will lvl enough so u can go further, w/o running low on mp. Also I have no idea of your gaming prowess, but its good to have a mix of DDs and mages, I myself have one mage and she is the heal type.